This project will examine the thesis that transposable elements are involved in each of four distinct, but still partially characterized, hypermutability systems in Drosophila ananassae. Three of these systems, previously defined largely in terms of dominant Minute mutation frequencies, will be assayed for other types of visible mutations; if the mutators (two chromosomal dominants ane one extrachromosomally transmitted element) are transposable elements, the assays of recovered mutants can be expected to expose differentially mutable loci and to include unstable mutant alleles. The fourth system is characterized by exclusive production of eye morphology (Om) mutants whose genetic properties suggest that an X-linked transposable element (tom) specifically inserts in control sequences shared by at least 15 structural genes involved in eye development. To confirm their genetic identity, Om mutants will be tested for X-ray induced reversion and for suppression by recessive eye defect mutants from other sources. The tom element will be assayed for its ability to secondarily transpose from an Om mutant to a new site and for its map relationship to Som mutants. Som mutants, recovered as suppressors of Om mutants and tentatively viewed as alternative forms of the tom element, will be subjected to tests for reversion by X-rays and for their ability to suppress mutants induced by the extrachromosomal mutator from which the integrated tom element may have arisen. It is expected that improved genetic definition of the ananassae hypermutability factors and of their interrelationships will contribute to the development of a general model relating transposable elements to spontaneous mutation mechanisms in eukaryotes.